云广直流特高压换流变压器短路阻抗的选择

由于±800kV云广特高压直流输电工程电压高、容量大且设备缺乏实际制造和运行经验,为合理选择换流变短路阻抗以限制最大可能短路电流在阀的承受水平又不使无功损耗增加和换相压降过大,分析了目前晶闸管的制造水平与性能参数及不同故障时换流阀能承受的最大可能短路电流,以云广特高压工程逆变侧穗东换流站为例,计算得出换流变压器的短路阻抗为(16~18)%。

Design of Converter Transformer Short Circuit Impedance in Yunguang UHVDC Project

Ultra high voltage direct current(UHVDC) power transmission systems are used in many countries in recent years.Until now,the highest voltage in commercial systems is 600 kV.However,it is a trend to increase the voltage level to 800 kV in the UHVDC power systems for larger amount of power and longer distance transmission.The design of Yunguang UHVDC project,from Yuanan to Guangdong Province,will be the first practical 800 kV UHVDC system in China and even in the world.Therefore,it is short of the manufacture and operational experience of this kind of UHVDC equipment.In this paper,the considerations in determining the short circuit impedance of a converter transformer are roughly introduced,that is a compromise on limiting the fault current in the valves and decreasing the var loss in the converter.The converter valves adopted in some other Chinese HVDC projects and the ones in Yunguang project are briefly mentioned.Then,with an analysis of the maximum endurable fault current in the converter valves during different faults,such as the bridge short-circuit fault, DC bus fault,commutation failure,fault turn-on and fail to turn-on,the maximum possible fault current through the converter transformer is obtained.Based on the manufacture technology and the performance parameters of these modern thyristory valves,together with the derived maximum fault current,the short circuit reactance could be calculated.Finally,taking the inverter side of the Huidong converter station as an example,the short circuit impedance of its converter transformer is computed and the final result is obtained involving certain margin.